Thomik Maximilian, Gruber Sebastian, Kaestner Anders, Foerst Petra, Tsotsas Evangelos, Vorhauer-Huget Nicole
Department of Thermal Process Engineering, Institute of Process Engineering, Otto-von-Guericke University Magdeburg, Universitaetsplatz 2, 39106 Magdeburg, Germany.
Department of Process Systems Engineering, TUM School of Life Sciences, Technical University of Munich, Gregor-Mendel-Str. 4, 85354 Freising, Germany.
Pharmaceutics. 2022 Jul 23;14(8):1538. doi: 10.3390/pharmaceutics14081538.
Freeze-drying frozen maltodextrin solutions with solid contents of 5% and 30% () was experimentally investigated using neutron imaging at PSI Villigen/Switzerland. Different solid contents, as well as annealing at -5 °C for 11 h, were used to modify the porous structure of the samples, which was quantified using X-ray computed tomography. Annealing of the 5% () sample, with a pore size distribution (PSD) of 23.7 ± 11.1 µm, yielded a very open pore space with high porosity (ε = 0.96) and a PSD of 33.0 ± 27.0 µm. In contrast, the higher solid content resulted in small, lamellar, narrow pores with high anisotropy and a porosity of ε = 0.65, as well as a PSD of 13.5 ± 4 µm. In operando neutron imaging was used to show the impact of the structure of frozen maltodextrin on the overall drying kinetics and shape of the sublimation front during freeze-drying. For this purpose, a freeze-drying stage was employed, which allowed a novel approach to time- and space-resolved monitoring of the ice phase. The sublimation front propagation was quantitatively analyzed based on ice saturation profiles and sublimation rates. The dependence of drying velocity on structure is nicely demonstrated by the data. In addition, it is shown that the sublimation front widened during freeze-drying, resulting in either rather concave or convex shape depending on morphological parameters.
在瑞士维利根的保罗·谢勒研究所（PSI），利用中子成像技术对固含量分别为5%和30%的冷冻麦芽糊精溶液进行冷冻干燥实验研究。通过不同的固含量以及在-5°C下退火11小时来改变样品的多孔结构，并用X射线计算机断层扫描对其进行量化。对固含量为5%的样品进行退火处理后，其孔径分布（PSD）为23.7±11.1µm，形成了具有高孔隙率（ε=0.96）的非常开放的孔隙空间，PSD为33.0±27.0µm。相比之下，较高的固含量导致形成小的、层状的、狭窄的孔隙，具有高各向异性，孔隙率为ε=0.65，PSD为13.5±4µm。在冷冻干燥过程中，采用原位中子成像来显示冷冻麦芽糊精的结构对整体干燥动力学和升华前沿形状的影响。为此，使用了一个冷冻干燥阶段，这使得一种对冰相进行时间和空间分辨监测的新方法成为可能。基于冰饱和度分布和升华速率对升华前沿的传播进行了定量分析。数据很好地证明了干燥速度对结构的依赖性。此外，结果表明，在冷冻干燥过程中升华前沿变宽，根据形态参数的不同，会形成相当凹或凸的形状。
